MXene-doped kapok fiber aerogels with oleophobicity for efficient interfacial solar steam generation

3-aminopropyltriethoxysilane modified MXene on three-dimensional nonwoven fiber substrates for low-cost, stable, and efficient solar-driven interfacial evaporation desalination

Recently, the solar-driven interfacial evaporation desalination has attracted more and more attentions due to the advantages of low cost, zero energy consumption, and high water purification rate, etc. One of the bottlenecks of this emerging technique lies in a lack of simple and low-cost ways to construct three-dimensional (3D) hierarchical microstructures for photothermal membranes. To this end, a two-step strategy is carried out by combining surface functionalization with substrate engineering. Firstly, a silane coupling agent 3-aminopropyltriethoxysilane (APTES) is grafted onto an ideal photothermal material of Ti3C2Tx MXene, to improve the nanochannel sizes and hydrophilicity, which are attributed to enlarged interspaces of MXene and introduced hydrophilic group e.g., -NH2 and -OH, respectively. Secondly, a low-cost and robust nonwoven fiber (NWF) substrate, which has a 3D micron-sized mesh structure with interlaced fiber stacks, is employed as the skeleton to load enough APTES-grafted MXene by a simple soaking method. Benefited from above design, the Ti3C2Tx-APTES/NWF composite membrane with a 3D hierarchical structure shows enhanced light scattering and utilization, water transport and vapor escape. A remarkable evaporation rate of 1.457 kg m-2 h-1 and an evaporation efficiency of 91.48 % are attained for a large-area (5 × 5 cm2) evaporator, and the evaporation rate is further increased to 1.672 kg m-2 h-1 for a small-area (2 × 2 cm2) device. The rejection rates of salt ions and heavy metal ions are higher than 99 % and 99.99 %, respectively, and the removal rates of organic dye molecules are nearly to 100 %. Besides, the composite photothermal membrane exhibits great stabilities in harsh conditions such as high salinities, long cycling, large light intensities, strong acid/alkali environments, and mechanical bending. Most importantly, the photothermal membrane shows a considerable cost-effectiveness of 89.4 g h-1/$. Hence, this study might promote the commercialization of solar-driven interfacial evaporation desalination by collaboratively considering surface modification and substrate engineering for MXene.

Hierarchical Ti3C2/BiVO4 microcapsules for enhanced solar-driven water evaporation and photocatalytic H2 evolution

Desalination processes frequently require a lot of energy to generate freshwater and energy, which depletes resources. Their reliance on each other creates tension between these two vital resources. Herein, hierarchical MXene nanosheets and bismuth vanadate (Ti3C2/BiVO4)-derived microcapsules were synthesized for a photothermal-induced photoredox reaction for twofold applications, namely, solar-driven water evaporation and hydrogen (H2) production. For this purpose, flexible aerogels were fabricated by introducing Ti3C2/BiVO4 microcapsules in the polymeric network of natural rubber latex (NRL-Ti3C2/BiVO4), and a high evaporation rate of 2.01 kg m-2 h-1 was achieved under 1-kW m-2 solar intensity. The excellent performance is attributed to the presence of Ti3C2/BiVO4 microcapsules in the polymeric network, which provides balanced hydrophilicity and broadband sun absorption (96 %) and is aimed at plasmonic heating with microscale thermal confinement tailored by heat transfer simulations. Notably, localized plasmonic heating at the catalyst active sites of the Ti3C2/BiVO4 heterostructure promotes enhanced photocatalytic H2 production evolved after 4 h of reaction is 9.39 μmol, which is highly efficient than pure BiVO4 and Ti3C2. This method turns the issue of water-fuel crisis into a collaborative connection, presenting avenues to collectively address the anticipated demand rather than fostering competition.

Insights on updates in sodium alginate/MXenes composites as the designer matrix for various applications: A review

Advancements in two-dimensional materials, particularly MXenes, have spurred the development of innovative composites through their integration with natural polymers such as sodium alginate (SA). Mxenes exhibit a broad specific surface area, excellent electrical conductivity, and an abundance of surface terminations, which can be combined with SA to maximize the synergistic effect of the materials. This article provides a comprehensive review of state-of-the-art techniques in the fabrication of SA/MXene composites, analyzing the resulting structural and functional enhancements with a specific focus on advancing the design of these composites for practical applications. A detailed exploration of SA/MXene composites is provided, highlighting their utility in various sectors, such as wearable electronics, wastewater treatment, biomedical applications, and electromagnetic interference (EMI) shielding. The review identifies the unique advantages conferred by incorporating MXene in these composites, examines the current challenges, and proposes future research directions to understand and optimize these promising materials thoroughly. The remarkable properties of MXenes are emphasized as crucial for advancing the performance of SA-based composites, indicating significant potential for developing high-performance composite materials.

Multifunctional Super-Hydrophilic MXene/Biomass Composite Aerogel Evaporator for Efficient Solar-Driven Desalination and Wastewater Treatment

Solar-driven interfacial evaporation is recognized as a sustainable and effective strategy for desalination to mitigate the freshwater scarcity issue. Nevertheless, the challenges of oil contamination, salt accumulation, and poor long-term stability of the solar desalination process limit its applications. Herein, a 3D biomass-based multifunctional solar aerogel evaporator is developed for water production with fabricated chitosan/lignin (CSL) aerogel as the skeleton, encapsulated with carbonized lignin (CL) particles and Ti3C2TiX (MXene) nanosheets as light-absorbing materials. Benefitting from its super-hydrophilic wettability, interconnected macropore structure, and high broadband light absorption (ca. 95.50%), the prepared CSL-C@MXene-20 mg evaporator exhibited a high and stable water evaporation flux of 2.351 kg m-2 h-1 with an energy conversion efficiency of 88.22% under 1 Sun (1 kW m-2) illumination. The CSL-C@MXene-20 mg evaporator performed excellent salt tolerance and long-term solar vapor generation in a 3.5 wt.% NaCl solution. Also, its super-hydrophilicity and oleophobicity resulted in superior salt resistance and anti-fouling performance in high salinity brine (20 wt.% NaCl) and oily wastewater. This work offers new insight into the manufacture of porous and eco-friendly biomass-based photothermal aerogels for advanced solar-powered seawater desalination and wastewater purification.

Natural lignocellulosic kapok fiber/MXene constructed hydrogel evaporators for high efficiency solar steam generation

Solar-driven interfacial evaporation (SDIE) is a green and sustainable technique for desalination. Hydrogel composite evaporators have been widely used for SDIE, but it is still challenging for the hydrogel evaporators to achieve uniform distribution of the light absorbing nanomaterials and at the same time possess satisfactory evaporation rate, durability and environmental applicability. We developed a 3D hydrogel evaporator with an asymmetric structure for high-efficiency SDIE. Natural kapok fibers, an important lignocellulosic plant fiber with a hollow structure, are decorated with MXene nanosheets for construction of one-dimensional photothermal conversion network. The top composite hydrogel serves as the light-absorption layer where MXene-modified kapok fibers are evenly dispersed in PVA hydrogel, while the bottom PVA hydrogel with an oriented structure acts as water delivery path. The evaporator exhibits a high solar evaporation rate and efficiency (2.49 kg·m-2·h-1 and 91.5 %, respectively) under one sun irradiation (1 kW·m-2). Even in a high salinity brine, emulsion and corrosive solutions, the evaporator can work normally with a slightly decreased evaporation rate. The 3D hydrogel evaporator with long-term stability and durability shows promising applications in purification of seawater and different waste water.

Improved solar-driven water purification using an eco-friendly and cost-effective aerogel-based interfacial evaporator with exceptional photocatalytic capabilities

As a promising solution to address the global challenge of freshwater scarcity, solar-powered interfacial steam generation has undergone notable advancements. This study introduces a novel solar-driven interfacial evaporation membrane (ZnIn2S4@SiO2/ACSA, ZSAS) comprising a ZnIn2S4@SiO2 composite and a black sodium alginate aerogel infused with activated carbon. The ZSAS membrane demonstrates exceptional light absorption and thermal insulation, leading to elevated surface temperatures and reduced heat dissipation into the bulk water. Furthermore, the incorporation of AC reinforces the mechanical properties of the ZSAS membrane and enhances the water purification performance. These collective features result in an impressive evaporation rate of 1.485 kg m-2 h-1 and a high photothermal conversion efficiency of 91.2% under 1 sun irradiation for the optimal ZSAS membrane. Moreover, the optimal ZSAS membrane can effectively remove salts, heavy metal ions, and organic pollutants, benefitting from its superior evaporation separation effect and the photocatalytic properties of the ZnIn2S4@SiO2 composite.

Natural down fiber-reinforced and polypyrrole-modified silk fibroin composite aerogel for efficient solar steam generation toward seawater desalination and wastewater treatment

Poor mechanical properties and low photothermal efficiency of silk fibroin (SF)-based aerogels are current challenges that need to be addressed. Herein, SF composite aerogel was developed to enhance the mechanical properties through physical interpenetration of natural down fiber (Df) and hydrogen bonds formed among SF, Df, and polypyrrole (PPy) and to improve the evaporation performance via in-situ polymerization of PPy. The resultant Df/PPy@SF aerogel showed significant improvement of compressive stress (194.29 kPa), which was 6.96 times than that of SF aerogel (27.91 kPa), and also good compression resiliency. Furthermore, due to uniform distribution of PPy and high porosity of 95.27 %, Df/PPy@SF aerogel possessed high light absorbance of 99.87 % and low thermal conductivity (0.043 W·m-1·K-1). Thus, the Df/PPy@SF aerogel evaporator demonstrated high evaporation rates of 2.12 kg·m-2·h-1 for 3.5 wt% saline water, 2.04-2.15 kg·m-2·h-1 for various dye water, and 2.10 kg·m-2·h-1 for actual dye wastewater. Moreover, the developed aerogel exhibited evaporation stability and outstanding salt-resistance when treating seawater due to continuous water supply by superhydrophilic porous aerogel. Therefore, these findings demonstrate the excellent performance of Df/PPy@SF aerogel and will inspire further research on developing natural fiber-reinforced aerogels for use in the fields of solar water evaporation, energy, and other related applications.

Distribution-according-to-work: Enhancing solar vapor generation of photothermal sponge by using cellulose-based water storage platform

Interfacial solar vapor generation (ISVG) has shown extraordinary promise in achieving high-efficiency water purification. However, the rapid water supply often leads to excessive water in the solar absorber, resulting in undesired heat loss and a decrease in evaporation rate. To tackle this issue, we developed a bio-based solar evaporator comprising cellulose-based water retention resin (CRR) and straw-derived photothermal sponge. CRR serves as an effective water storage platform with a high binding capacity for water molecules, preventing water from entering the absorber and reducing the water evaporation enthalpy. The water management of CRR confines the solar-to-vapor conversion to the interface between CRR and the photothermal sponge, thereby eliminating the adverse effects of excess water. Additionally, the ISVG process operates based on the principle of Distribution-according-to-work, meaning that the quantity of generated vapor depends on the evolution of the sponge structure. Optimal sponge configuration enables evaporation rates of 2.28 and 1.53 kg/m2/h under solar irradiation of 1.0 and 0.5 kW/m2, respectively. Additionally, the obtained evaporator is capable of producing 7.1 kg/m2/day of freshwater in outdoor experiment. This report proposes a novel approach to designing an ISVG device that incorporates effective water management strategy for achieving high-efficiency water purification in real-world scenarios.

Hanging Photothermal Fabric Based on Polyaniline/Carbon Nanotubes for Efficient Solar Water Evaporation

Solar-driven water evaporation is essential to provide sustainable and ecofriendly sources of fresh water. However, there are still great challenges in preparing materials with broadband light absorption for high photothermal efficiency as well as in designing devices with large evaporation areas and small heat dissipation areas to boost the water evaporation rate. We designed a hanging-mode solar evaporator based on the polyaniline/carbon nanotube (PANI/CNT) fabric, in which the photothermal fabric acts as the solar evaporator and the micropores on the cotton fabric act as the water transfer channels. The hanging mode provides efficient evaporation at both interfaces by greatly reducing the heat dissipation area. The hanging mode PANI/CNT fabric solar evaporator can achieve an evaporation rate of 2.81 kg·m-2·h-1 and a photothermal efficiency of 91.74% under a solar illumination of 1 kW·m-2. This high-performance evaporator is designed by regulating the photothermal material and evaporation device, which provides a novel strategy for sustainable desalination.

Highly efficient MoS2/MXene aerogel for interfacial solar steam generation and wastewater treatment

Interfacial solar steam generation using aerogels holds great promise for seawater desalination and wastewater treatment. However, to achieve aerogels with both durable, high-efficiency evaporation performance and excellent salt resistance remains challenging. Here, a molybdenum disulphide (MoS2) and MXene composite aerogel with vertical pore channels is reported, which has outstanding advantages in mechanical properties, water transportation, photothermal conversion, and recycling stability. Benefiting from the plasmon resonance effect of MXene and the excellent photothermal conversion performance of MoS2, the aerogel exhibits excellent light absorption (96.58 %). The aerogel is resistant to deformation and able to rebound after water absorption, because of the support of an ordered vertical structure. Moreover, combined with the low water evaporation enthalpy, low thermal conductivity, and super hydrophilicity, the aerogel achieves an efficient and stable evaporation rate of about 2.75 kg m-2h-1 under one sun and exhibits excellent self-cleaning ability. Notably, the evaporator achieves removal rates of 99.9 % for heavy metal ions and 100 % for organic dyes, which has great potential in applications including seawater desalination and wastewater purification.

Starch hydrogel with Poly(ionic liquid)s grafted SiO2 for efficient desalination and wastewater purification

Solar-driven interface evaporation is promising to alleviate the fresh water scarcity in an economical and sustainable way. However, most of currently reported photothermal conversion materials (PMs) are time-consuming costly, inefficient, or complex preparation process, which causes low utilization efficiency, and difficult to be practical for large-scale application. To solve this problem, a facile and green strategy for preparing hydrogel evaporator (SiO2-PILs/starch) by grafting poly(ionic liquid)s onto silica and doping it with starch is proposed. Benefiting from the broad solar absorption (ca.91 %), strong hydrophilic, and superb salt tolerance and stain resistance of SiO2-PILs/starch. Under 1 sun irradiation, the SiO2-PILs/starch achieves a remarkable solar evaporation efficiency of 91.72 % in pure water and 81.45 % in 20 wt% NaCl solution, respectively. In particular, SiO2-PILs/starch exhibited outstanding long-term salt stability (8 h) and crystalline salt can be self-cleaned in the dark environment. It is worth noting that the prepared hydrogel also possesses a satisfied evaporation efficiency of 75.84 % in oily wastewater (3 wt% n-hexadecane solution) due to its excellent water retention. These properties of SiO2-PILs/starch may provide desperately needed solution for efficient desalination and guaranteed high applicability and durability in practice.

Plant Transpiration-Inspired Biomass-Based Device with Underwater Oleophobicity for Efficient General-Purpose Solar-Driven Oily Wastewater Purification

The remediation of wastewater containing oily pollutants is imperative to mitigate the serious threats posed to the safety of fresh water, human well-being, and the environment. Current membrane separation technologies are severely restricted by their limitations for separating various types of oily pollutants with low sustainability. Herein, by imitating the plant transpiration in nature, we designed a solar-driven device composed of natural biomass sugar cane stem, chitosan/carboxymethyl cellulose, and graphite powders to separate versatile oily pollutants from the wastewater. Owing to its superior solar absorption capacity, microchannels for water transportation, and underwater oleophobicity, the resultant evaporator not only exhibited an excellent evaporation rate of 1.41 kg m-2 h-1 but also demonstrated an admirable purification efficiency of 99.9% for oily wastewater. Moreover, the device can maintain a stable evaporation rate and the original structure even in oily wastewater containing strong acid, alkali, or hypersaline components. Therefore, this work provides an effective approach to producing clean water from versatile wastewater.

Removal and reuse of heavy metal ions on mildly oxidized Ti3C2 @BF membrane via synergistic photocatalytic-photothermal approach

The pollution of heavy metal ions in water seriously affects the ecosystem and human health. Here, an efficient synergetic photocatalytic-photothermal system is designed by combining a mildly oxidized Ti3C2 (mo-Ti3C2) with a super hydrophilic bamboo fiber (BF) membrane. The mo-Ti3C2 heterojunction promotes the transfer and separation of photoinduced charges and thus enhances the photocatalytic reduction of heavy metal ions (Co2+, Pb2+, Zn2+, Mn2+ and Cu2+). The photoreduced metal nanoparticles with high conductivity and LSPR effect further accelerate the transfer and separation of photoinduced charges, and improve photothermal and evaporative performance. The mo-Ti3C2-2.4 @BF membrane in Co(NO3)2 solution can achieve an excellent evaporation rate of 4.6 kg·m-2·h-1 and a high solar-vapor efficiency of up to 97.5% under the light intensity of 2.44 kW·m-2, which are 27.8% and 19.6% higher than those in H2O, respectively, demonstrating the reuse of photoreduced Co nanoparticles. No heavy metal ions are detected in any of the condensed water, and the Co2+ removal rate in the concentrated Co(NO3)2 solution is up to 80.4%. The synergetic photocatalytic-photothermal approach on the mo-Ti3C2 @BF membrane provides a new scope for the continuous removal and reuse of heavy metal ions, as well as for obtaining clean water.

2D MXenes Embedded Perovskite Hydrogels for Efficient and Stable Solar Evaporation

Solar evaporation is a facile and promising technology to efficiently utilize renewable energy for freshwater production and seawater desalination. Here, the fabrication of self-regenerating hydrogel composed of 2D-MXenes nanosheets embedded in perovskite La 0.6Sr 0.4Co 0.2Fe 0.8O3- δ (LSCF)/polyvinyl alcohol hydrogels for efficient solar-driven evaporation and seawater desalination is reported. The mixed dimensional LSCF/Ti3C2 composite features a localized surface plasmonic resonance effect in the polymeric network of polyvinyl alcohol endows excellent evaporation rates (1.98 kg m-2 h-1) under 1 k Wm-2 or one sun solar irradiation ascribed by hydrophilicity and broadband solar absorption (96%). Furthermore, the long-term performance reveals smooth mass change (13.33 kg m-2) during 8 h under one sun. The composite hydrogel prompts the dilution of concentrated brines and redissolves it back to water (1.2 g NaCl/270 min) without impeding the evaporation rate without any salt-accumulation. The present research offers a substantial opportunity for solar-driven evaporation without any salt accumulation in real-life applications.

Low temperature-resistant superhydrophobic and elastic cellulose aerogels derived from seaweed solid waste as efficient oil traps for oil/water separation

Aerogel has excellent application potential in adsorption, heat preservation, and other areas due to its typical advantages of low density and high porosity. However, there are several issues with the use of aerogel in oil/water separation, including weak mechanical qualities and challenges in eliminating organic contaminants at low temperature. Inspired by cellulose Iα, which has excellent performance at low temperature, this study used cellulose Iα nanofibers extracted from seaweed solid waste as the skeleton, through covalent cross-linked with ethylene imine polymer (PEI) and hydrophobic modification of 1, 4-phenyl diisocyanate (MDI), supplemented by freeze-drying technology to form three-dimensional sheet, and successfully obtained cellulose aerogels derived from seaweed solid waste (SWCA). The compression test shows that the maximum compressive stress of SWCA is 61 kPa, and the initial performance still maintains 82% after 40 cryogenic compression cycles. In addition, the contact angles of water and oil on the surface of the SWCA were 153° and 0°, respectively, and the stable hydrophobic time in simulated seawater is more than 3 h. By combining the elasticity and superhydrophobicity/superoleophilicity, the SWCA with an oil absorption capacity of up to 11-30 times its mass, might be utilized repeatedly for the separation of an oil/water mixture.

Cellulose-based evaporator with dual boost of water transportation and photothermal conversion for highly solar-driven evaporation

Two-dimensional (2D) evaporation systems could significantly reduce the heat conduction loss compared with the photothermal conversion materials particles during the evaporation process. But the normal layer-by-layer self-assembly method of 2D evaporator would reduce the water transportation performance due to the highly compact channel structures. Herein, in our work, the 2D evaporator with cellulose nanofiber (CNF), Ti₃C₂T_x (MXene) and polydopamine modified lignin (PL) by layer-by-layer self-assembly and freeze-drying methods. The addition of PL also enhanced the light absorption and photothermal conversion performance of the evaporator due to the strong conjugation and π-π molecular interactions. After the combination process of layer-by-layer self-assembly and freeze-drying process, the as-prepared freeze-dried CNF/MXene/PL (f-CMPL) aerogel film exhibited highly interconnected porous structure with promoted hydrophilicity (enhanced water transportation performance). Benefiting these favorable properties, the f-CMPL aerogel film showed enhanced light absorption performance (surface temperature could be reached to 39 °C under 1 sun irradiation) and higher evaporation rate (1.60 kg m^-2 h^-1). This work opens new way to fabricate cellulose-based evaporator with highly evaporation performance for the solar steam generation and provides a new idea for improving the evaporation performance of 2D cellulose-based evaporator.

MXene/polypyrrole coated melamine-foam for efficient interfacial evaporation and photodegradation

The application of photothermal materials in seawater desalination, wastewater treatment have been widely studied, however, there are relatively few studies that combine photothermal effects and solar-driven photocatalysis and exhibit efficient solar-driven water evaporation performance and excellent photocatalytic ability. Form the perspective of practical application, it is of great significance to combine photothermal effect with solar-driven photocatalysis to develop environment-friendly evaporator with low cost, simple preparation process and ability of seawater desalination, wastewater treatment and photodegradation of organic dyes. In this paper, a novel multifunctional MXene/polypyrrole (PPy) coated melamine foam (MF) named as MF-MXene/PPy was successfully prepared by simple impregnation and in-situ polymerization. The MF-MXene/PPy has rich porosity (89.13 %), abundant water molecule transport channels, excellent light absorption capacity (about 94 %), low thermal conductivity (0.1047 W m^-1 K^-1), and exhibits excellent performance in solar desalination, wastewater purification and photodegradation of organic dyes. Under 1 kW m^-2 illuminate, the solar energy conversion rate and efficiency of MF-MXene/PPy reaches up to 1.5174 kg m^-2h^-1 and 91.24 %. Moreover, due to the regular pore size of MF-MXene/PPy, good salinity tolerance was shown even after continuous evaporation in 20 wt% NaCl for 8 h. After continuous evaporation in 70 mL of 20 wt% NaCl for 8 h, the amount of salt collected could reach 0.2 g. In addition, MF-MXene/PPy also possessed excellent visible light degradation ability for organic dyes, and the degradation rate of methylene blue (MB), rhodamine B (RHB) and methyl orange (MO) were 92.38 %, 88.92 % and 91.75 %, respectively. As a fundamental research, this research will open a novel way to the development of new evaporator.